As a way of counteracting the anthropogenic emissions of carbon dioxide to the atmosphere, the removal of carbon dioxide – Carbon Capture and Storage (CCS) – is widely discussed today. However, injections of carbon dioxide into the subsurface of the earth is a process that has been undertaken since the early 1970s, explains Gry Møl Mortensen, state geologist at the Geological Survey of Sweden with responsibility for work with CCS in Sweden.

“This is not a new technique, it is a well-known and mature technique”, she says.

The earth’s crust consists of different layers of different materials with different characteristics. Carbon dioxide can be injected for example to depleted oil or gas reservoirs, coal seams or to saline aquifers, which are underground water-bearing, porous and permeable layers of sedimentary rock. In order to keep the carbon dioxide in a fluid phase, the reservoir needs to be situated at 800 meters depths or more.

“You can pretty much imagine the process in the reservoir rock like a sponge sucking up water and holding the water”, explains Gry Møl Mortensen.

On top of the porous layer, there should be a dense and thick layer of for example shale or clay stone, a caprock that functions as a “lid” preventing the carbon dioxide to migrate to the surface. At places where all these parameters are fulfilled, carbon dioxide can be transported by ship to a platform, under which there are pipelines and wellheads facilitating the injection deep below the seabed.

 

Eight suitable areas in the Baltic Sea

Eight potential storage units for carbon dioxide have been identified in the southern Baltic Sea, that fulfil the geological conditions and have an estimated storage capacity of more than 100 million tonnes each. SGU has recently received a large governmental assignment to investigate the areas further, something that will take several years.

"It is very important to have very thorough investigations of the rocks, and we also need to have test injection to analyse the behaviour of the CO2", emphasises Gry Møl Mortensen.

However, some international conventions might constitute obstacles to the implementation of CCS in these areas, such as the Helsinki convention that prohibits the dumping of garbage on the seafloor, to which carbon dioxide could be considered.

“It sounds as if there are no really major problems from the geological perspective, is that so?”, asks moderator Gun Rudquist.

“Well, if you do the pre-work very thoroughly and assure that you have the distributions and the right porosity and the cap rocks have the conditions that you want – then there is no problem”, says Gry Møl Mortensen.

As for the ecological consequences, she refers to a project that have simulated injected carbon dioxide sipping out in the water. 

“As far as I know nothing happened, nature adapts”, says Gry Møl Mortensen.

 

The sediment can be a gold mine – for iron and manganese

Another way of exploring the earth below the sea is through seabed mining, which is also a hot topic in today’s debate. The modern society is dependent on the supply of some rare earth minerals, of which some are essential for electrification and thereby the transition to a low-carbon economy. It has turned out that some areas in the northern Baltic Sea are rich on the so-called iron manganese nodules and there is now commercial interest in exploring these nodules.

“These are basically rock like formations that are rich in iron, manganese, phosphorus and other rare minerals like copper and cobalt. These nodules are more or less the size of a potato”, says Francisco Nascimento, Associate Professor and researcher at Department of Ecology, Environment and Plant Sciences, Stockholm University.

The company Scandinavian Ocean Minerals has applied for permit to mine the seabed outside Skellefteå for the iron manganese nodules. The plan is to use an airlift technique, which Francisco Nascimiento explains as basically vacuum cleaning the upper 5-10 centimetres of the sea floor. The sediment is brought up to a platform at the surface of the sea where it’s being sieved. The particles larger than one millimetre are kept and the remains are released back to the sea floor.

“This will create plumes or clouds of sediment that will settle down”, adds Francisco Nascimento who is about to start a research project to evaluate the environmental effects of seabed mining in the Baltic Sea.

 

 

All animal groups are affected – recovery differs

Until now, the effects of seabed mining have mainly been investigated in the deep sea, as this is where large deposits of these nodules are found. An experiment of disturbance of the sea floor at 4000 meters depth showed effects on all types of benthic animals.

For animals larger than one centimetre (megafauna), the disturbance showed to have strong immediate impact on the abundance.

“After seven years it hasn't still returned to the baseline”, says Francisco Nascimento.

For the smaller group of animals, the impact is similar but the recovery tend to be shorter. 

“So the main takeaway message here is that we is that we have impacts, strong impacts at the beginning at all sizes of fauna, but there is different recovery potentials depending on the size of the animals”, says Francisco Nascimento

 

Impact on bacterial functions

In another study, the recovery of even smaller organisms; bacteria, was monitored. 

“When the intensity of the disturbance is high, the number some bacteria are significantly lower than in the reference area. And this is even after 26 years afterwards.” 

The researchers also looked at not only the number of bacteria, but also their activity and capacity to degrade carbon compounds. 

“And there we see also an impact, after 26 years, this function performed by bacteria is not back.”

 

Expected effects on Baltic ecosystem

In a new large research project funded by research council Formas, that will start off this spring, Francisco Nascimento and his colleagues will look into how the coastal ecosystems in the Baltic Sea will react to the same type of pressures.

“We expect significant impacts on benthic biodiversity. I think we if you if you vacuum clean the first 5 to 10 centimetres, it's a reasonable expectation that biodiversity will be impacted.
But we are also interested in how fast the system recover and if the trajectories of recovery are different for the different types of communities.”

The research will also study the impacts of mining on ecosystem functions, like the carbon and nitrogen cycle.

“Because we will re-mobilise a lot of carbon that has been sequestered in the deeper layers of the sediments, there is a potential that greenhouse gas fluxes from these sediments will increase”, says Francisco Nascimento.

The goal of the project is to improve the ecological risk assessment tools that can help managers to evaluate the risks of seabed mining.

“I hope that we will have time to carry out this project before large scale exploration happens. I think there is a large interest from authorities to regulate this type of activities, that we have more information and build better ecological risk assessment”, says Francisco Nascimento.

Text: Lisa Bergqvist

 

Answers to questions from the audience

Carbon Capture and Storage

So far you show possibilities and talk about profitability. However, what are the environmental impacts and risks? It's a maritime installation after all. What about impact of the actual installation, the additional ship traffic, underwater noise, input of chemicals, energy needed etc.

Gry Møl Mortensen: Of course, an installation for CO2 storage will have an impact, comparable to an offshore windfarm. For CO2 leakage in the marine environment and environmental monitoring, you can learn more at: https://www.stemm-ccs.eu/ 

What is the energy cost of pumping CO2 into the ground? I presume pressure builds the more you pump down, so at some point it’s not energy efficient to do so?

Gry Møl Mortensen: This is a little out of my area but I recommend you to seek more information from ongoing CCS project in for example Norway: https://norlights.com/, https://ccsnorway.com/project-outcomes/ 

So, 5+3 possible storing sites, 100 Mt CO2 = 800 Mt. 40 Mt/year is the Swedish emission rate. => ~20 years of emissions. Correct?

Gry Møl Mortensen: Well, I’m afraid it’s not that simple, if you look at my slide nr 15 you can see examples of static estimates for capacity, but as I mentioned in the talk you need also to do dynamic estimates based on a comprehensive data set. You can read more of this in reports from the NORDICCS project I mentioned: NordiCCS - Nordic CCS Competence Centre , or in some of SGU:s reports, for example: Koldioxidlagring i Sverige
– sammanställning och resultat från NORDICCS, Geologisk lagring av koldioxid i Sverige
och i grannländer – status och utveckling

CCS- the talk is about storing, not capturing. What is the present level of capture CO2 worldwide in terms of Mt?

Gry Møl Mortensen: This is developing fast, but I think you should be able to find new data in the Global CCS Institute: www.globalccsinstitute.com

Seabed mining

What quantities of CO2 were released during the tests on the effects on marine ecosystems? 

Francisco Nascimento: As far as I know this as not been investigated in relation to coastal mining. We know a bit more about the effects of other similar types of disturbances to the seabed, as for example trawling. Trawling of the seafloor has been show to increase carbon re-mineralization, which results in higher CO2 production (see Anthropogenic disturbance keeps the coastal seafloor biogeochemistry in a transient state) and higher methane fluxes to the water (see: Physical Disturbance by Bottom Trawling Suspends Particulate Matter and Alters Biogeochemical Processes on and Near the Seafloor).

The Baltic is in a bad condition. We are not talking about a blank area. How are the accumulated effects?

Francisco Nascimento: The areas being considered for mining are in reasonably good environmental health. There is however some data that indicates that there are significant quantities of pollutants like metals (eg: chromium, arsenic and mercury that might be remobilized after sediment disturbance due to mining (see: Miljöföroreningar i utsjösediment – geografiska mönster och tidstrender. We are preparing to apply for funding to add this aspect to the project 

Have there been any projects trying to rebuild the soil ecosystem after DSM disturbed it? If so what results did they show?

Francisco Nascimento: There is quite a bit of research done on habitat restoration of terrestrial ecosystems after mining activities (see: How can we restore biodiversity and ecosystem services in mining and industrial sites?. To my knowledge this has not been attempted in marine environments, also because mining activities have not started yet on a large scale. But, in my opinion, such restoration efforts on land would be hard to transfer to marine habitats because of the intrinsic differences between these two types of ecosystems.

How can seabed mining in the Baltic be planned if the environmental impacts are definitely there...?

Francisco Nascimento: As discussed in the seminar we do not know the extent of the impacts and how long the recovery will take. In addition, the alternative scenarios have to be weighed in: What are the environmental impacts of extracting these minerals on land? What is the environmental cost of a slower transition to a low carbon emitting economy in the context of climate change. We need data to be able to balance all these questions.

@Francisco you didn't mention resuspension of nutrients. I assume that would also be an issue?

Francisco Nascimento: Yes, you are correct. The nutrient fluxes from the sediment are likely to increase. We are planning to quantify this possible increase, and the time it takes to return to a normal baseline.

 

See the whole seminar: